Question

An express train goes past a man and a platform 396 m long in 12 seconds and 30 seconds respectively. What is the speed of the express train?

• A. 75.2 km/hr
• B. 79.2 km/hr
• C. 83.2 km/hr
• D. 81.6 km/hr
• E. None of these

Answer 1

The correct option is B

79.2 km/hr

Let x be the length of the train and v be the speed.

Time taken to move past the man = 12 s=> $\frac{x}{v}$ = 12 => x = 12v --- (1)

Time taken to cross the platform 396 m long = 30 s

$\frac{x+396}{v}$= 30 => x + 396 = 30v --- (2)

Substituting equation 1 in equation 2, we get

12v +396 = 30v => v = $\frac{396}{18}$ = 22 m/s

=> v = 22$\times$$\frac{18}{5}$ kmph = 79.2 kmph